So what I'm working on is a spring reverb as is probably clear by now. I used the transducer + amplifier (the little board on the car/sled) from a
Paper Jamz guitar amplifier, the spring from a (toy) echo microphone and a piezo pickup connected to a preamp I found in my box of old circuits.
While I was thinking about how to construct it I got the idea to make one end of the spring adjustable to control the length/tension. The next idea
was to control it with a servo. At first I thought it was just a silly idea, but I gave it go to see if I could do it. I used some curtain rails + rollers
to make the adjustable part and then figured out a way to control it with the servo. I already had a simple servo tester to control it with which
was my original plan, but since a servo is pulse width controlled it's pretty easy to make that voltage controlled.
I'll post the circuit for that + more info later._________________"My perf, it's full of holes!"http://phobos.000space.com/SoundCloudBandCampAcidTrasHStickney Synthyards

TRANSDUCER:
As mentioned I used the transducer from a Paper Jamz guitar amplifier. It's just a cardboard box with an amplifier design printed on it and there's
a plastic battery compartment on the back which also has the input jack and power on/off switch + LED. I expected that there would be a small
speaker inside but to my surprise it was a transducer glued to the cardboard. It basically is a speaker but it uses the front of the box
as a "cone". (someone posted some photos of it here).

I needed a way to connect the spring to it and my first idea was to drill some small holes in the little cardboard cilinder that has the coil on it.
Then bend a little wire that goes through the holes which I could hook the spring on. For my first tests I drilled 2 small holes and simply left the drill
in so I could attach the spring to it. This worked pretty well but I wasn't really happy that it left the gap between the magnet and voicecoil
exposed, and I found something better. A little plastic 'thingy' that I just glued onto the cilinder (which has a plastic ring on top) and I drilled a
hole in it to hold the spring.

AMPLIFIER:
Driving the transducer was easy because it came with an amplifier. I used an old 5v phonecharger to power it since it needs 4.8V..6V (4 batteries),
and also because it uses more current than I would like to pull from my main PSU. It had a stereoinput jack but only one transducer so I took a
look at the PCB to see how they were mixed together. I found out that there's a capacitor and resistor in series with each input, and the resistors
are attached together at one input of the chip. I didn't see anything else connected to it so I guess it's just a passive resistor mixer. I also noticed
that there was a 100 ohm resistor to ground on each input. This might have something to do with what it's originally intended for but I removed
them. I also removed the capacitor and resistor from one input and the connector which gave me space to solder on a small trimpot to adjust the
input level.

I replaced the standard red LED with a bright blue one which is mounted in such a way that it illuminates the spring and piezo disc. Both the
transducer and amplifier are mounted on the "sled" so the LED moves up and down too.

Back in my day, I think the most specialized LEGO piece was the one you could stick a wheel in. No people.

Now maybe they even have VCO, VCF, VCA pieces .

I think they went a bit too far with the specialized pieces, there are a lot of parts now that seem to be made for only one purpose. It's like
playmobil. I haven't seen any synth stuff yet but I have thought about making a LEGO modular. The LEGO part would just be the case, panels
and knobs that are made of LEGO with some synth circuits behind it. Also standard 5mm LED's fit perfect in LEGO technics holes (that's actually
what got me started with electronics ) and you could use gears and a motor to modulate pots.
hmm, a mechanically patchable synth by attaching gears instead of patchcables.
anyway, that's too expensive for me to build right now, but it's an idea,.._________________"My perf, it's full of holes!"http://phobos.000space.com/SoundCloudBandCampAcidTrasHStickney Synthyards

I used the two sinewave oscillators connected to the waveshaper and the output of that was connected to the spring reverb. It starts with one
oscillator, then the level of the other oscillator is slowly turned up. At ± 55secs in the spring reverb is added and it get's adjusted at ±1:10. It
produces some springy sounds at a certain point not sure why,. It's almost as if it get's stuck for a second, but I can't find it so it's just a bonus sound.
I also adjusted it rapidly a couple times and then you can hear the servo aswell. The final design has a glide function for smooth transitions.
At the very end you can here some vibrations caused by the servo which it does above a certain point to fight the string tension (at least I think that's
what causes it). So I also added an on/off switch to silence the servo, but more on that when I get to the control circuit.

THE SPRING:
I used a spring from an "echo mic' which is a plastic toy in the shape of a microphone. It has a thin plastic cup inside with the spring attached to
it, so when you speak into the microphone it vibrates the spring and causes an echo effect. Here's how they look:

There's not much to say about it except that its a very nice spring for a springreverb

PIEZO PICKUP:
I wasn't sure how to attach the spring and mount the piezo disk. I was thinking of drilling 2 holes in the disk one for the spring and one on
the opposing side for another spring to keep the piezo in place. Or one hole for the spring and then glue the disc onto some foam or rubber.
So I looked for some DIY springreverbs on the web and saw a couple a versions that had the spring soldered directly to the piezo. So I gave that
a try which wasn't easy. The solder didn't stick to the spring and it's already bad solder to begin with (not sure if it is leadfree but it behaves
the same). After a while I got it stuck on there but wasn't sure if the piezo had survived all the heat.,. so I tested it and it worked
I drilled two holes in the disc and mounted it in a similar way as Gijs Gieskes did.

PREAMP:
The preamp came from my box of old circuits. It was a microphone/MD preamp of which I had only build the microphone section. It was made
for a single supply using a fake ground so I made some changes to the circuit to use it with a dual supply. I noticed I could faintly hear the sine
wave VCO's so I added resistors and capacitors to the power line to filter out any noise.

I think they went a bit too far with the specialized pieces, there are a lot of parts now that seem to be made for only one purpose. It's like
playmobil.

I would respectfully disagree. There are some very creative people out there working out how to use those specialized pieces for very sculptural works. Check out The Brothers Brick sometime if you want to see real jaw dropping LEGO work.

PHOBoS wrote:

I haven't seen any synth stuff yet but I have thought about making a LEGO modular. The LEGO part would just be the case, panels
and knobs that are made of LEGO with some synth circuits behind it. Also standard 5mm LED's fit perfect in LEGO technics holes (that's actually
what got me started with electronics ) and you could use gears and a motor to modulate pots.
hmm, a mechanically patchable synth by attaching gears instead of patchcables.
anyway, that's too expensive for me to build right now, but it's an idea,..

ah yes I remember that one, I like that you can build a 3D sculpture .
I will check out the brothers brick. What I do think is nice nowadays is that
you can use software to design and then just order the parts you need
(and share the designs online)._________________"My perf, it's full of holes!"http://phobos.000space.com/SoundCloudBandCampAcidTrasHStickney Synthyards

SERVO CONTROLLER:
So I got this silly idea of making the spring adjustable and voltage controlled (thanks brain ). When I first tested the servo with the
tester it worked fine, but when I tried to control it with a circuit consisting of a triangle wave oscillator + comparator it started to behave very
randomly. It was actually quite fun to watch but not exactly what I had in mind. (I might have a recording of it). Turned out that it was caused by
the servo causing noise in the powerline eventhough I was using a seperate supply for it, but then again that one isn't very powerful.
Also the servo moves to one end position with a pulsewidth of 1mS and the other end at 2mS which translated to a control voltage of only 2mV.

So I did a couple of things. Instead of using the same 5v powersupply as I used for the servo I used the dual main supply and added some regulators
for a more stable dual voltage of +/- 5 V. Besides a more stable voltage this also increases the amplitude of the saw wave which in turn increases the
range of the control voltage. It's still pretty small though.

For the CV input I used the same setup as used for the waveshaper, with offset control, level control and limiters (so the servo isn't forced to move
beyond it's range). I also added a glide control for smoother movement which makes it possible to modulate it with a slow square wave aswell.
I used an optocoupler to keep it isolated from the servo supply to prevent any noise. There's also a switch to turn the control signal off which halts
the servo (it doesn't move by the spring tension). This can also be controlled by an external signal which can work as a sample track and hold together
with the CV input.

Besides the springreverb I also mounted a passive tonecontrol circuit on the same panel. It also came from my box of circuits and it's something I
took out of an old amplifier many years ago. Because it is passive it just has 2 inputs and 2 outputs and no active components, so I just added 4
connectors for the inputs and outputs. I wired the output from the reverb to the left input by using the switch contact on the socket and wired the
input of the reverb to the right channel also using the switch contact. This turns the balance control into a sort of wet/dry control when the outputs
are mixed together. The in-/outputs of the reverb also have attenuators to adjust the levels.

I used foam on the top and bottom of the reverb chamber to dampen vibrations from the case and I also used rubber grommets between the
panel and chamber for the same reason. I had to cut a bit off to be able to get it mounted in the case and this left a gap which I simply covered
with a piece of masking tape.

Here's the finished module

Frankensynth spring reverb - 02.jpg

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Frankensynth spring reverb

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Frankensynth spring reverb

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Frankensynth spring reverb - 04.jpg

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Frankensynth spring reverb (backside)

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Frankensynth spring reverb - 09.jpg

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Frankensynth spring reverb (powerboard for servo & amplifier and foam on the bottom)

Looks and sounds amazing! The grille looks nice too, although I thought you may have wanted direct access to the spiring for plucking it.

thanks

yeah plucking the spring was a reason why I wasn't sure about the grille (I can still remove it btw). But plucking the grille gives a similar sound,
without overdriving the preamp. And I still have more springs and piezo's which I could use for a springboard anyway._________________"My perf, it's full of holes!"http://phobos.000space.com/SoundCloudBandCampAcidTrasHStickney Synthyards

great work I love the sound of the reverb malfunctioning, if your Cv is too high for it, why not just put it through a voltage divider?_________________As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"

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